The present invention relates to a motor-driven fuel pump having a substantially cylindrical pump casing, a motor section provided in the pump casing, and a pump section adapted to be driven by the motor section for pumping up fuel through the motor section to the outside of the pump casing. More particularly, it relates to such a motor-driven fuel pump wherein the motor section includes a commutator which contacts a brush extending in an axial direction of the motor section.
In such a motor-driven fuel pump, it is intended to reduce its outer diameter by arranging the brush so as to extend in the axial direction of the motor section is disclosed in Japanese Patent Laid-open Publication Nos. 63-272994 and 63-243489, for example.
FIG. 6 shows a construction of such a pump as disclosed in the above prior art. Referring to FIG. 6, reference numeral 101 designates a substantially cylindrical pump casing which accommodates a pump section 160 at a lower portion thereof and a motor section 170 at a middle portion thereof.
The pump section 160 includes two lower covers 107 and 108 between which a space 161 is defined. An impeller 111 is rotatably provided in the space 161. The two lower covers 107 and 108 are formed with fuel passages 113 and 112, respectively, communicating with the space 161. When the impeller 111 is rotated, fuel is sucked from the fuel entry passage 112, and is then discharged under pressure from the fuel outlet passage 113.
The motor section 170 is primarily composed of a cylindrical stator 104 fixed to an inner perephery of the pump casing 101 and an armature 103 surrounded by the stator 104. The armature 103 is rotated by motor shaft 105 which is rotatably supported at its upper and lower ends. The lower end of the motor shaft 105 is connected to the impeller 111.
Two separate covers 106a and 106b are provided to cover the upper end of the motor section 170. The first cover 106a is formed with an opening 109a for mounting a bearing 109 therein, an opening 116 for accommodating a brush 115, and a cup-shaped depression 118 for accommodating a choke coil 117. The first cover 106a is mounted over the motor section 170, the bearing 109 is fixedly mounted in the opening 109a, and the brush 115 is inserted into the opening 116 against the biasing force of a spring 124. The upper end of the motor shaft 105 is supported by the bearing 109, and the brush 115 is brought into contact with a commutator 123 fixed to an upper end of the armature 103.
Two metal plates 150 and 151 are fixed on the upper surface of the first cover 106a. After inserting the brush 115 into the opening 116 and inserting the choke coil 117 into the cup-shaped depression 118, a pig tail shaped conductor 128 of the brush 115 is connected to one end 150b of the metal plate 150, and one end 117a of the choke coil 117 is connected to the other end 150a of the metal plate 150, while the other end 117b of the choke coil 117 is connected to the metal plate 151.
After the completion of the above mentioned operations, the second cover 106b is mounted over the first cover 106a. Then, a terminal rod 121 is inserted into the second cover 106b, and one end 121a of the terminal rod 121 is connected to the metal plate 151.
Thus, a conducting line from the terminal rod 121 through the choke coil 117 and the brush 115 to the commutator 123 is formed.
In the above prior art pump, the assembly of the upper end of the motor section 170 with the first and second covers 106b and 106a, and the number of parts requires too many operations.
Furthermore, it is necessary to prevent the brush 115 from being pushed out of the opening 116 due to the biasing force of the spring 124 during the mounting operation of the first cover 106a over the motor section 170. Even though the second cover 106b is assembled with the first cover 106a before the former is mounted over the motor section 170, the above problem cannot be eliminated.